Allozyme Variation within and between Populations of Coreopsis intermedia (Asteraceae)

Abstract Enzyme electrophoresis was used to measure genetic diversity in two populations of Coreopsis intermedia of section Coreopsis , a rare species endemic to a small area of Texas and Louisiana. Genetic diversity is higher in C. intermedia than has been reported for many other geographically restricted species. C. intermedia contains levels of genetic variation comparable to those of other species in section Coreopsis , and a greater amount of diversity than either the rare congener, C. latifolia (section Silphidium ), or the Florida endemic, C. leavenworthii (section Calliopsis ). The two populations, although greatly different in size, exhibited similar levels of genetic diversity.     

Differences in population structure of the anther smut fungus Microbotryum violaceum on two closely related host species, Silene latifolia and S. dioica

We investigated the genetic population structure of the sexually transmitted plant pathogen, the fungus Microbotryum violaceum, on the two closely related host species Silene latifolia and S. dioica using microsatellite markers. We found strong deviations from Hardy-Weinberg expectations, with significant heterozygote deficiency in almost all populations. Fungal strains from the two host species were differentiated, and these host races differed in amount of variation within populations and differentiation among populations. Anther smut from S. latifolia harboured significantly less microsatellite diversity and were more genetically differentiated from each other than those from S. dioica. Small effective population sizes, rapid population turnover, and less gene flow among populations could lead to this higher population differentiation and lower within population genetic diversity for anther smut populations on S. latifolia than on S. dioica. These results are in concordance with host ecology because S. latifolia grows in more disturbed habitats than S. dioica and may provide a shorter-lived host environment.     

Genetic and clonal diversity of two cattail species, Typha latifolia and T. angustifolia (Typhaceae), from Ukraine

Genetic and clonal diversity vary between two closely related cattail species (Typha angustifolia and T. latifolia) from Ukraine. This diversity was calculated from microsatellite data. Forty-eight percent of the total variation was partitioned between species, which formed distinct clusters in a dendrogram with no indication of hybrid populations. Typha angustifolia had higher heterozygosity at the species (H(es) = 0.66) and population (H(ep) = 0.49) levels than did T. latifolia (H(es) = 0.37 and H(ep) = 0.29, respectively). The higher number of alleles in T. angustifolia may be indicative of larger effective population sizes due to its higher seed production. Clonal diversity of T. angustifolia was lower than that of T. latifolia (N(g)/N(r) = 0.40 and 0.61, Simpson's D = 0.82 and 0.94, respectively). Correlations between clonal and genetic diversity were higher for T. latifolia than T. angustifolia, suggesting that the importance of factors and their interactions affecting this relationship are different for the two species. Latitudinal and longitudinal trends were not observed in either species despite the large sampling area. Population differentiation was relatively high with F(ST) of 0.24 and 0.29 for T. angustifolia and T. latifolia, respectively. Weak isolation by distance was observed for T. latifolia but not for T. angustifolia.     

Hierarchical Analysis of Nucleotide Diversity in Geographically Structured Populations

Existing methods for analyzing nucleotide diversity require investigators to identify relevant hierarchical levels before beginning the analysis. We describe a method that partitions diversity into hierarchical components while allowing any structure present in the data to emerge naturally. We present an unbiased version of NEI's nucleotide diversity statistics and show that our modification has the same properties as WRIGHT's F(ST). We compare its statistical properties with several other F(ST) estimators, and we describe how to use these statistics to produce a rooted tree of relationships among the sampled populations in which the mean time to coalescence of haplotypes drawn from populations belonging to the same node is smaller than the mean time to coalescence of haplotypes drawn from populations belonging to different nodes. We illustrate the method by applying it to data from a recent survey of restriction site variation in the chloroplast genome of Coreopsis grandiflora.     

Plant generalization on pollinators: species property or local phenomenon?

Despite recent increased interest in the frequency and evolutionary consequences of generalization in plant-pollinator systems, little is known on whether plant generalization on pollinators actually is a species-level trait. This paper addresses the following questions for the insect-pollinated shrub Lavandula latifolia: (1) Are different populations of this pollinator-generalist plant similarly generalized? (2) Within a highly generalized population, are all plants similarly pollinator-generalists? Comparable values for richness in pollinator species were obtained from individual- or population-specific rarefaction curves as the projected number of distinct pollinator species implicated in 100 flower visits (S(RAR100)). Simple counts of pollinator species recorded per individual or population (S(OBS)) were weakly or nonsignificantly correlated with corresponding S(RAR100) figures and closely correlated with flower visitation frequency. The pollination system of L. latifolia was highly generalized at the regional level, but populations differed greatly in pollinator species richness (S(RAR100)). Within the population intensively studied, individual plants had quite variable degrees of generalization, comparable in magnitude to variation among populations. It is concluded that generalization was not an invariant, species-level property in L. latifolia. Furthermore, pollinator diversity estimates based on S(OBS) data may be heavily contingent on aspects related to both research design (sampling effort) and biological phenomena (variation in pollinator abundance or visitation rates), which may either mask or distort underlying ecological patterns of interest.     

Genetics of cattails in radioactively contaminated areas around Chornobyl

Research on populations from radioactively contaminated areas around Chornobyl has produced ambiguous results for the presence of radiation effects. More studies are needed to provide information on whether radiation exposure at Chornobyl significantly affected genetic diversity in natural populations of various taxa. Eleven and nine variable microsatellite loci were used to test for differences in genetic diversity between reference and Chornobyl populations of two cattail species (Typha angustifolia and Typha latifolia, respectively) from Ukraine. Our purpose was to determine whether radiation had a significant impact on genetic diversities of the Chornobyl Typha populations, or if their genetic composition might be better explained by species demography and/or changes in population dynamics, mainly in sexual and asexual reproduction. Populations closest to the reactor had increased genetic diversities and high number of genets, which likely were due to factors other than radiation including increased gene flow among Chornobyl populations, enhanced sexual reproduction within populations, and/or origin of the genets from seed bank. Both Typha species also demonstrated small but significant effects associated with latitude, geographical regions, and watersheds. Typha's demography in Ukraine possibly varies with these three factors, and the small difference between Chornobyl and reference populations of T. latifolia detected after partitioning the total genetic variance between them is probably due primarily to these factors. However, the positive correlations of several genetic characteristics with radionuclide concentrations suggest that radiation may have also affected genetics of Chornobyl Typha populations but much less than was expected considering massive contamination of the Chornobyl area.     

Genetic variation and clonal diversity in four clonal sedges (Carex) along the Arctic coast of Eurasia

We studied the structure of genetic variation (at both ramet- and genet-level) and clonal diversity within and among populations in the four closely related arctic clonal sedges Carex bigelowii, C. ensifolia, C. lugens and C. stans by use of allozyme markers. Compared to other sedges and arctic plants, the studied taxa all had high levels of genetic variation, both within populations and taxa. These taxa contained most of the total gene diversity (H(T)) within populations and a small part of the diversity among populations (G(ST) ranged 0.05--0.43). Carex bigelowii had genetic variation (H(S) = 0.173, mean for populations) at a comparable level to other outbreeding arctic plants and to other widespread, rhizomatous and mainly outbreeding Carex species. In contrast, C. ensifolia (H(S) = 0.335), C. lugens (H(S) = 0.339) and C. stans (H(S) = 0.294) had within-population variations that were higher than in most other studied Carex species and for arctic plants in general. Genetic variation was not related to any tested environmental variable, but it was lower in areas deglaciated only 10,000 years BP compared to areas deglaciated 60,000 years BP or not glaciated at all during the Weichselian. All the populations were multiclonal, except for two populations of C. stans that were monoclonal. In contrast to genetic variation, clonal diversity decreased with latitude and did not differ between areas with different times of deglaciation. In accordance with previous studies, C. bigelowii and C. lugens were found to be outbreeding, while C. ensifolia and C. stans had mixed mating systems.     

Capturing Genetic Variation during Ecological Restorations: An Example from Kankakee Sands in Indiana

Genetic variation in populations, both natural and restored, is usually considered crucial for response to short‐term environmental stresses and for long‐term evolutionary change. To have the best chance of successful long‐term survival, restored populations should reflect the extant variation found in remnants, but restored sites may suffer from genetic bottlenecks as a result of founder effects. Kankakee Sands is a large‐scale restoration being conducted by The Nature Conservancy (TNC) in northwestern Indiana. Our goal was to test for loss of genetic variation in restored plant populations by comparing them with TNC’s seed source nursery and with local remnant populations that were the source of nursery seed and of the first few restored sites. Allozyme analysis of Baptisia leucantha, Asclepias incarnata, Coreopsis tripteris, and Zizia aurea showed low levels of allozyme diversity within all species and reductions in polymorphism, alleles per locus, and expected heterozygosity between remnants and restorations for all species except A. incarnata. Almost all lost alleles were rare; restored populations contained almost 90% of alleles at polymorphic loci that occurred in remnants at frequencies greater than 1%. Allele frequencies for most loci did not differ between remnants and restored sites. Most species showed significant allele frequency differentiation among remnant populations and among restored sites. Our results indicate that seed collection techniques used at Kankakee Sands captured the great majority of allozyme variation present in seed source remnant populations.     

Indirect evidence from DNA sequence diversity for genetic degeneration of the Y-chromosome in dioecious species of the plant Silene: the SlY4/SlX4 and DD44-X/DD44-Y gene pairs

The action of natural selection is expected to reduce the effective population size of a nonrecombining chromosome, and this is thought to be the chief factor leading to genetic degeneration of Y-chromosomes, which cease recombining during their evolution from ordinary chromosomes. Low effective population size of Y chromosomes can be tested by studying DNA sequence diversity of Y-linked genes. In the dioecious plant, Silene latifolia, which has sex chromosomes, one comparison (SlX1 vs. SlY1) indeed finds lower Y diversity compared with the homologous X-linked gene, and one Y-linked gene with no X-linked homologue has lower species-wide diversity than a homologous autosomal copy (SlAp3Y vs. SlAp3A). To test whether this is a general pattern for Y-linked genes, we studied two further recently described X and Y homologous gene pairs in samples from several populations of S. latifolia and S. dioica. Diversity is reduced for both Y-linked genes, compared with their X-linked homologues. Our new data are analysed to show that the low Y effective size cannot be explained by different levels of gene flow for the X vs. the Y chromosomes, either between populations or between these closely related species. Thus, all four Y-linked genes that have now been studied in these plants (the two studied here, and two previously studied genes, have low diversity). This supports other evidence for an ongoing degeneration process in these species.     

Adding a third dimension to the edge of a species' range: altitude and genetic structuring in mountainous landscapes

In addition to the topographical and ecological barriers, other landscape features may also subtly influence the patterns of gene flow and spatial genetic structuring at species' borders. This paper focuses on the role played by altitudinal gradients that characterize mountainous landscapes. We formulate and test the hypothesis that when the distribution boundaries of plant species intersect mountainous landscapes, altitudinal gradients in ecological conditions may considerably enhance population subdivision and genetic structuring at the regional level. Using amplified fragment length polymorphism markers, we studied genetic diversity and differentiation in a set of 21 peripheral populations of the evergreen shrub Lavandula latifolia Med. (Labiatae) at its southernmost distribution limit in the Betic mountain ranges of southern Spain. Population size and abundance, and within-population genetic diversity, varied predictably with altitude, being highest at middle elevations and declining steadily towards both the upper and lower altitudinal distribution margins. Genetic differentiation tended to follow the opposite trend. These altitudinal patterns result from variation with elevation in the relative influence of gene flow and drift on the distribution of genetic variation. Genetic drift prevails around the upper and lower altitudinal limits, whereas a situation closer to a drift-gene flow equilibrium exists at the center of the altitudinal distribution. Altitudinal variation in the relative influences of gene flow and drift appears as an essential element in the interpretation of regional genetic structuring of L. latifolia at its mountainous distribution edge, and a factor which may influence the evolutionary potential of peripheral populations and the likelihood of local adaptation.     

Population structure and genetic diversity in four tropical tree species in Costa Rica

Despite intensified interest in conservation of tropical forests, knowledge of the population genetics of tropical forest trees remains limited. We used random amplified polymorphic DNA (RAPD) data to evaluate trends in genetic diversity and differentiation for four tropical tree species, Alchornea latifolia, Dendropanax arboreus, Inga thibaudiana and Protium glabrum . These species occur at contrasting population densities along an elevational gradient and we use RAPD and ecological data to examine natural levels of genetic diversity of each species, trends in genetic variability with population density and structure, genetic differentiation along the elevation gradient, and the relationship between genetic diversity and such factors as seed dispersal and pollination syndrome. At the distances we examined (plot distances ranging from 0.8 to 8.6 km) there was very little genetic structuring at any distance along the gradient. All four species exhibited levels of variation expected for spatial distribution, mating system and pollinator syndrome; greater than 96% of the genetic variation occurred within plots for Inga thibaudiana, Protium glabrum and Dendropanax arboreus. Alchornea latifolia only occurred in a single plot. The results of this study contribute to a growing database of genetic diversity data that can be utilized to make predictions about the effect of disturbance and subsequent reductions in population size on genetic variation and structure in tropical tree species.     

Population genetic structure of two rare tree species (Colubrina oppositifolia and Alphitonia ponderosa,Rhamnaceae) from Hawaiian dry and mesic forests using random amplified polymorphic DNA markers

Hawaiian dry and mesic forests contain an increasingly rare assemblage of species due to habitat destruction, invasive alien weeds and exotic pests. Two rare Rhamnaceae species in these ecosystems, Colubrina oppositifolia and Alphitonia ponderosa, were examined using random amplified polymorphic DNA (RAPD) markers to determine the genetic structure of the populations and the amount of variation relative to other native Hawaiian species. Relative variation is lower than with other Hawaiian species, although this is probably not a consequence of genetic bottleneck. Larger populations of both species contain the highest levels of genetic diversity and smaller populations generally the least as determined by number of polymorphic loci, estimated heterozygosity, and Shannon's index of genetic diversity. Populations on separate islands were readily discernible for both species as were two populations of C. oppositifolia on Hawai'i island (North and South Kona populations). Substructure among Kaua'i subpopulations of A. ponderosa that were ecologically separated was also evident. Although population diversity is thought to have remained at predisturbance levels, population size continues to decline as recruitment is either absent or does not keep pace with senescence of mature plants. Recovery efforts must focus on control of alien species if these and other endemic dry and mesic forest species are to persist.     

RAPD Profiling in Detecting Genetic Variation in Endemic Coelonema (Brassicaceae) of Qinghai-Tibet Plateau of China

Random amplified polymorphic DNA (RAPD) markers were used to measure genetic diversity of Coelonema draboides (Brassicaceae), a genus endemic to the Qilian Mountains of the Qinghai-Tibet Plateau. We sampled 90 individuals in 30 populations of Coelonema draboides from Datong and Huzhu counties of Qinghai Province in P.R. China. A total of 186 amplified bands were scored from the 14 RAPD primers, with a mean of 13.3 amplified bands per primer, and 87% (161 bands) polymorphic bands (PPB) was found. Analysis of molecular variance (AMOVA) shows that a large proportion of genetic variation (84.2%) resides among individuals within populations, while only 15.8% resides among populations. The species shows higher genetic diversity between individuals than other endemic and endangered plants. The RAPDs provide a useful tool for assessing genetic diversity of rare, endemic species and for resolving relationships among populations. The results show that the genetic diversity of this species is high, possibly allowing it to adapt more easily to environmental variations. The main factor responsible for the high level of differentiation within populations and the low level of diversity among populations is probably the outcrossing and long-lived nature of this species. Some long-distance dispersal, even among far separated populations, is also a crucial determinant for the pattern of genetic variation in the species. This distributive pattern of genetic variation of C. draboides populations provides important baseline data for conservation and collection strategies for the species. It is suggested that only populations in different habitats should be studied and protected, not all populations, so as to retain as much genetic diversity as possible.     

渐危植物浙江楠群落结构及叶片性状多样性

浙江楠为商品材“金丝楠木”的原植物之一,天然分布区窄,属国家二级保护渐危种,在全球气候变化背景下,研究其天然种群所在森林群落的结构特征及其多样性具有重要意义.本研究以浙江楠天然分布区内13个典型种群为对象,研究其所在群落的群落结构特征、物种多样性和叶片表型变异特征.结果表明: 浙江楠天然种群所在群落的结构复杂,物种多样性较高,13个群落的16块样地内共有维管束植物87科162属235种,其中种子植物79科151属221种;重度干扰导致浙江开化、浙江临安等群落的乔木层物种多样性指数显著低于其他群落,而中度干扰提高了福建建宁群落灌木层物种多样性,轻度干扰则利于浙江楠种群自然更新.叶片表型作为楠木属植物重要的分类依据,叶片表型性状在种群间、种群内均存在丰富变异,平均变异系数为17.2%,变异幅度为10.4%～27.5%.种群间的变异(53.6%)大于种群内的变异(17.0%),平均表型分化系数为75.1%,种群间变异是浙江楠叶片表型变异的主要来源.基于欧式距离(10 cm)将13个天然种群划分为两大类群,但变异呈随机性.     

Geographic pattern of genetic variation in Pinus resinosa: area of greatest diversity is not the origin of postglacial populations

Genetic diversity is low in natural populations of red pine, Pinus resinosa, a species that has a vast range across north-eastern North America. In this study, we examined 10 chloroplast microsatellite or simple sequence repeats (cpSSR) loci in 136 individuals from 10 widespread populations. Substantial variation for the cpSSR loci was observed in the study populations. The contrast with red pine's lack of variation for other types of loci is likely to be due to the higher mutation rates typical of SSR loci. The amount of variation is lower than that generally found for cpSSR loci in other pine species. In addition, the variation exhibits a striking geographical pattern. Most of the genetic diversity is among populations, with little within populations, indicating substantial isolation of and genetic drift within many populations in the southern half of the species distribution. The greatest diversity now occurs in the north-eastern part of New England, which is especially intriguing because this entire area was glaciated. Thus the centre of diversity cannot be the origin of postglacial populations, rather it is likely caused by admixture, most probably because of influences from two separate refugia. Furthermore, the pattern indicates that the spread of red pine since the last glaciation is rather more complex than usually described, and it likely includes more than one refugia, complex migration routes, and postglacial-retreat isolation and genetic drift among shrinking populations in regions of the present southern range.     

宽叶兔儿风花序侧生分枝的变异式样以及分枝兔儿风的分类地位问题

宽叶兔儿风Ainsliaealatifolia花序主轴上的侧生分枝通常被描述为由单个或2–4个头状花序聚集而组成的簇生花序。作者在野外和标本馆中仔细研究了该种居群内侧生分枝花序形态的变异,依据其简化和集中的程度在居群内区分出3种花序类型:简单的复合聚伞花序、复杂的复合聚伞花序以及两者之间的过渡类型,具有后面两种类型的个体在居群内少见。这一发现不仅为探讨兔儿风属内各种花序的演化提供了新的线索,而且为理清宽叶兔儿风这一地理广布种的分类学问题提供了新的视野。居群内有些侧生分枝为复杂的复合聚伞花序类型的个体整个花序的主轴折断了,这是由于整个主轴顶端部分被昆虫蛀食或者其他外力造成的。值得注意的是分枝兔儿风Ainsliaealatifoliavar.ramifera的主模式就属于这种情况。分枝兔儿风和宽叶兔儿风原变种之间在分布区、生境以及物候上并没有明显的分化,因此分枝兔儿风被处理成宽叶兔儿风的异名。     

Host-related genetic differentiation in the anther smut fungus Microbotryum violaceum in sympatric, parapatric and allopatric populations of two host species Silene latifolia and S. dioica

We investigated genetic diversity in West European populations of the fungal pathogen Microbotryum violaceum in sympatric, parapatric and allopatric populations of the host species Silene latifolia and S. dioica, using four polymorphic microsatellite loci. In allopatric host populations, the fungus was highly differentiated by host species, exhibiting high values of F(ST) and R(ST), and revealed clear and distinct host races. In sympatric and parapatric populations we found significant population differentiation as well, except for one sympatric population in which the two host species grew truly intermingled. The mean number of alleles per locus for isolates from each of the host species was significantly higher in sympatric/parapatric than in allopatric populations. This suggests that either gene flow between host races in sympatry, or in case of less neutral loci, selection in a more heterogeneous host environment can increase the level of genetic variation in each of the demes. The observed pattern of host-related genetic differentiation among these geographically spread populations suggest a long-term divergence between these host races. In sympatric host populations, both host races presumably come in secondary contact, and host-specific alleles are exchanged depending on the amount of fungal gene flow.     

The evolution and maintenance of monoecy and dioecy in Sagittaria latifolia (Alismataceae)

Plant species rarely exhibit both monoecious and dioecious sexual systems. This limits opportunities to investigate the consequences of combined versus separate sex function on mating patterns and genetic variation and the analysis of factors responsible for the evolution and maintenance of the two sexual systems. Populations of the North American clonal aquatic Sagittaria latifolia are usually either monoecious or dioecious and often grow in close geographic proximity. We investigated mating patterns, genetic structure, and relationships between the two sexual systems using allozyme variation in populations from southern Ontario, Canada. As predicted, selfing rates in monoecious populations (n = 6, mean = 0.41) were significantly higher than in dioecious populations (n = 6, mean = 0.11). Moreover, marker-based estimates of inbreeding depression (delta) indicated strong selection against inbred offspring in both monoecious (mean delta = 0.83) and dioecious (mean delta = 0.84) populations. However, the difference in selfing rate between the sexual systems was not reflected in contrasting levels of genetic variation. Our surveys of 12 loci in 15 monoecious and 11 dioecious populations revealed no significant differences in the proportion of polymorphic loci (P), number of alleles per locus (A), or observed and expected heterozygosity (H(o) and H(e), respectively). Strong inbreeding depression favoring survival of outcrossed offspring may act to maintain similar levels of diversity between monoecious and dioecious populations. Despite geographical overlap between the two sexual systems in southern Ontario, a dendrogram of genetic relationships indicated two distinct clusters of populations largely corresponding to monoecious and dioecious populations. Reproductive isolation between monoecious and dioecious populations appears to be governed, in part, by observed differences in habitat and life history. We suggest that selfing and inbreeding depression in monoecious populations are important in the transition from monoecy to dioecy and that the maintenance of distinct sexual systems in S. latifolia is governed by interactions between ecology, life history, and mating.     

Allozyme Variation and Genetic Relationships among Species of Cimicifuga (Ranunculaceae) from Korea

Allozyme investigation of the five Cimicifuga taxa in Korea was conducted to assess genetic and clonal diversity within populations and genetic divergence among populations and taxa. Levels of allozyme variation maintained in Korean Cimicifuga taxa were comparable to those for most herbaceous perennials. In general, samples excluding copies of the same multilocus genotype maintained higher levels of genetic diversity than the total samples within populations. Copies of homozygous genotypes at several loci resulting from clonal spread lead to decreased levels of genetic diversity within populations, indicating that clonal reproduction found in Cimicifuga affects population genetic structure. In general, more widely distributed species such as C. dahurica and C. japonica harbored higher levels of allozyme diversity than the other taxa examined. Although two varieties of C. heracleifolia are geographically and reproductively isolated, the genetic and clonal structure of var. bifida seems to resemble var. heracleifolia, indicating that the two varieties may have had a similar evolutionary history. However, the allozyme data strongly indicate that the two morphological types (Groups I and II) of C. simplex should be treated as separate species.     

内蒙古高原小叶锦鸡儿(Caragana microphylla)、中间锦鸡儿(C. davazamcii)和柠条锦鸡儿(C. korshinskii)的遗传多样性及遗传关系

采用RAPD技术对10个具较大地理跨度的小叶锦鸡儿、中间锦鸡儿和柠条锦鸡儿种群的遗传多样性和遗传关系进行了研究.共检测到678个位点,多态条带比率(PPB)为100%;特有位点41个,占6.05%.总体上3种锦鸡儿的遗传多样性表现出自东向西递减的趋势,分析表明其与生长地点年均气温呈显著负相关.AMOVA表明:3种锦鸡儿种间变异只占总体变异的6.08%,且显著性检验表明这种变异不显著;种内种群间的变异占总变异的11.90%;总变异的主要部分来自种群内部(82.02%). 3种锦鸡儿各种群总体分析结果表明:种群内变异比率Hpop/Hsp为0.8013,基因分化系数Gst为0.1603,种群每代迁移数Nm为2.6192,显示种群间存在一定强度的基因流,3种锦鸡儿间表现为异交性.3种锦鸡儿多样性高低及种群聚类分布格局都表现出一定的地理连续性.